Lecture 5 - The Peripheral Nervous System

Question 1

What kind of neurons does the Somatic Nervous System contain? (voluntary)

Answer 1

• sensory neurons (afferent)
• somatic motor neurons (efferent)

Question 2

What do sensory neurons do?

Answer 2

convery input from receptors for somatic senses and receptors for special senses

Question 3

What do somatic motor neurons do?

Answer 3

innervate skeletal muscles

Question 4

What does the autonomic nervous system do? (involuntary)

Answer 4

• regulates cardiac muscle, smooth muscle, and glandular tissue
• autonomic motor neurons regulate visceral activities by exciting or inhibiting activities in effector tissue

Question 5

Somatic sensory vs visceral sensory (afferent divison of PNS)

Answer 5

• somatic sensory: carries signals from receptors in skin, muscles, bones and joints
• visceral sensory: carries signals mainly from organs in the thoracic and abdominal cavities

Question 6

How many neuron systems are there in the somatic vs autonomic nervous system?

Answer 6

• somatic: 1
• autonomic: 2

Question 7

Somatic neuron system

Answer 7

starts at spinal cord -> somatic motor neuron -> effector (skeletal muscle)

Question 8

Autonomic neuron system

Answer 8

starts at spinal cord -> preganglionic neuron - > ganglion -> postganglionic neuron -> effectors (smooth muscle, glands, cardiac muscle)

Question 9

General sensory receptors by structural class

Answer 9

• free nerve endings
• encapsulated
• proprioceptors

Question 10

Free nerve ending: of sensory neurons: functional class by stimulus type

Answer 10

• nociceptors (pain)
• thermoreceptors (heat and cold)
• mechanoreceptors (pressure)
• chemoreceptors (changes in chemical compositions)

Question 11

Free nerve ending: of sensory neurons: body location

Answer 11

• most of the body tissue; most dense in connective tissue

Question 12

Modified free nerve endings: (Merkel discs): functional class by stimulus type

Answer 12

mechanoreceptors (light pressure)

Question 13

Modified free nerve endings: (Merkel discs): body location

Answer 13

deepest layer of epidermis

Question 14

Free nerve endings: hair follicle receptors: functional class by stimulus type

Answer 14

mechanoreceptors (hair deflection)

Question 15

Free nerve endings: hair follicle receptors: body location

Answer 15

in and surrounding hair follicles

Question 16

Encapsulated: tactile (meissner’s) corpuscles: functional class by stimulus type

Answer 16

• mechanoreceptors (light pressure, discriminative touch, vibration of low frequency)

Question 17

Encapsulated: tactile (meissner’s) corpuscles: body location

Answer 17

hairless skin, particularly nipples, external genitalia, fingertips, eyelids

Question 18

Encapsulated: lamellar (pacinian) corpuscles: functional class by stimulus type

Answer 18

• mechanoreceptors (deep pressure, stretch, vibration of high frequency)

Question 19

Encapsulated: lamellar (pacinian) corpuscles: body location

Answer 19

• dermis and hypodermis; most abundant on fingers, soles of feet, external genitalia, nipples

Question 20

Encapsulated: ruffini corpuscles: functional class by stimulus type

Answer 20

• mechanoreceptors (deep pressure and stretch)

Question 21

Encapsulated: ruffini corpuscles: body location

Answer 21

deep in dermis, hypodermis and joint capsules

Question 22

Proprioceptors: muscle spindles: functional class by stimulus type

Answer 22

mechanoreceptos (muscle stretch)

Question 23

Proprioceptors: muscle spindles: body location

Answer 23

skeletal muscles; particularly those of the extremitites

Question 24

Proprioceptors: tendon organs: functional class by stimulus type

Answer 24

mechanoreceptos (tendon stretch)

Question 25

Proprioceptors: tendon organs: body location

Answer 25

tendons

Question 26

What are the purposes of the spinal cord? (4)

Answer 26

- communication system between brain and various parts of the body - essential for voluntray and involuntary actions - highways for sensory and motor integrations - important for rapid automatic responses through reflexes

Question 27

What are the roles of the spinal cord?

Answer 27

- provide structural support - protection - organization of nerves

Question 28

What are the 3 layers of the spinal cord (from outside layer to inside the nerve fiber)

Answer 28

- epineurium - perineurium - endoneurium

Question 29

How many pairs of spinal nerves are there?

Answer 29

31

Question 30

What is special about spinal nerve pairs 1-7?

Answer 30

they leave the spinal cord above their corresponding vertebrae level

Question 31

Classify the 31 spinals nerves into their groups

Answer 31

- 8 pairs of cervicle nerves - 12 pairs of thoracic nerves - 5 pairs of lumbar nerves - 5 pairs of sacral nerves - 1 pair of coccygeal nerves

Question 32

What do each spinal nerves connect to the spinal cord throuhg?

Answer 32

dorsal root

Question 33

What do dorsal roots contain?

Answer 33

- axonal processes of sensory neurons arising from posterior horn - dorsal root ganglion

Question 34

What is the dorsal root ganglion?

Answer 34

- enlargment of dorsal root - cluster of cell bodies of sensory neurons - functions as sensory relay stations by processing and modulating sensory signal before reaching the CNS

Question 35

Where do the spinal nerve and the dorsal root ganglion lie within?

Answer 35

the intervertebral foramina

Question 36

What does the ventral root contain?

Answer 36

- axonal processes of motor neurons whose cell bodies are locted in the anterior horn of the spinal cord

Question 37

What does each spinal nerve branch into? (2)

Answer 37

- dorsal ramus or - ventral ramus

Question 38

What do the dorsal and ventral rami have in common?

Answer 38

- contain sensory and motor fibers - exit the vertebral column through the intervertebral foramina - supply the entire somatic region of the body

Question 39

What are the differences between dorsal and ventral rami?

Answer 39

- dorsal rami: supplies dorsum of neck and back - ventral rami: supplies andterior and lateral regions of neck and truck, and all regions of the limbs. It is also much thicker than the dorsal rami

Question 40

How do the ventri rami travel?

Answer 40

- they brand out extensively to form complex networks known as nerve plexuses (rather than travelling directly to their target issue)

Question 41

How many primary nerve plexues are there from the ventral rami?

Answer 41

4 the nerve travel to specific target tissue to facilitate motor control and sensory perception

Question 42

What are the nerve plexuses of the body?

Answer 42

- cervical - brachial - lumbar - sacral

Question 43

Cervicle plexus

Answer 43

- spinal nerves C1-C4 - supplies sensory and motor innervation to the neck and portions of the head

Question 44

Bracial plexus

Answer 44

- spinal nerves C5-T1 - supplies sensory and motor innervation to shoulders and upper limbs

Question 45

lumbar plexus

Answer 45

- spinal nerves L1-L4 - supplies nerves to the lowerback, abdominal wall, and part of the lower limb

Question 46

Sacral plexus

Answer 46

- spinal nerves L4-S5 - innervates the buttocks, pelvic structures and the remainder of the lower limbs

Question 47

What are dermatomes?

Answer 47

- sections of the skin innervated by a single spinal nerve - motor and sensory innervation for those specific areas

Question 48

what are th etwo important dermatomes?

Answer 48

- T4: nipples - T10: Umbillicus

Question 49

Anatomy of the motor reflex arc

Answer 49

1. sensory recptor 2. sesnory neuron (afferent) 3. dorsal root ganglion 4. dorsal root 5. posteior horn 6. interneurons 7. anterior horn 8. motor neuron (efferent) 9. effector muscle